JP4145473B2 - Surface light source device and liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a light guide used in a mode in which the traveling direction of light supplied from the side is changed internally and emitted from the emission surface. Board Used surface light source device And In addition, the present invention relates to a liquid crystal display device in which such a surface light source device is employed for lighting of a liquid crystal display panel, particularly for front lighting.
[0002]
[Prior art]
A surface light source device of a type in which light is introduced from a side end surface of a light guide plate and one of two major surfaces (surface having a larger area than the end surface) of the light guide plate is used as an output surface is, for example, a liquid crystal display device Widely used for back lighting and front lighting. The basic performance of this type of surface light source device largely depends on the light guide plate used.
[0003]
The basic role of the light guide plate is to change the traveling direction of light introduced into the light guide plate from the side end surface (substantially parallel to the light exit surface of the light guide plate) and emit the light from the light exit surface. As is well known, if a simple transparent plate is used as it is, the direction is hardly changed and sufficient luminance cannot be obtained. Therefore, a means for promoting emission from the emission surface is required.
[0004]
Means for promoting the emission of the light guide plate are (1) scattering power inside the light guide plate (scattering light guide plate), (2) light diffusing exit surface (one major surface), (3) light diffusing back surface, It is supported by a method of any one of (4) an exit surface having a refractive uneven shape, or (5) a back surface having a refractive uneven shape, or a combination thereof.
[0005]
The method (1) is easy to obtain high-efficiency and uniform outgoing light. However, the preferential emission direction from the emission surface is greatly inclined from the front direction (usually, an inclination of about 60 to 75 degrees with respect to the normal line standing on the emission surface). Therefore, an element (prism sheet) for correcting the direction in the front direction is required. Even if the light diffusing sheet is used, the light in the front direction increases to some extent, but light diffusion occurs in a wide range and the energy efficiency is lowered.
[0006]
In the methods (2) and (3), it is difficult to obtain outgoing light with high efficiency. Further, similarly to the method (1), the emission from the emission surface strongly occurs obliquely. Increasing light diffusivity does not increase efficiency due to factors such as wide-range scattering and absorption by light diffusing elements (white ink, etc.).
[0007]
The method (4) facilitates the escape of light from the exit surface, but it cannot be said that a positive direction change is performed. Therefore, it is difficult to obtain outgoing light with high efficiency. In particular, it is not advantageous that light traveling from the back surface of the light guide plate toward the exit surface is not generated.
[0008]
The method (5) positively generates light traveling from the back surface of the light guide plate to the exit surface, and does not cause wide-range scattering. Therefore, there is a possibility that emitted light having directivity that goes in a direction close to the front direction can be efficiently generated.
[0009]
Furthermore, there is an advantage that it is relatively excellent in applicability to a front light type liquid crystal display device which has been frequently used in recent years.
However, in practice, the conventional technique has not been sufficient to control the traveling direction of the outgoing light from the outgoing surface.
[0010]
Fig.1 (a)-FIG.1 (c) are the figures explaining the application example of the method of said (5). In the figure, reference numeral 1 denotes a light guide plate made of a transparent material such as acrylic resin, and one side end surface thereof provides an incident end surface 2. The primary light source L is disposed in the vicinity of the incident end face 2 and supplies light to the incident end face 2. One of the two major surfaces 3 and 4 of the light guide plate 1 is an emission surface 3. The other surface (referred to as “rear surface”) is provided with a large number of recesses 5 having a cross-sectional shape having inclined surfaces 5a and 5b.
[0011]
The light emitted from the primary light source L is introduced into the light guide plate 1 through the incident end face 2. When light propagating in the light guide plate 1 (represented by light rays G 1 and G 2) encounters the recess 5, it is internally reflected by one inclined surface 5 a and directed toward the exit surface 3. θ is an internal incident angle, and G1 ′ and G2 ′ are outgoing lights corresponding to the light beams G1 and G2. Thus, the slope 5a closer to the incident end face 2 (primary light source L) than the other slope 5b provides an internal reflection slope for changing the direction. Such an action is sometimes called an edge lighting effect.
[0012]
The recess 5 is formed in a dot shape or a line groove shape. Further, as shown in FIGS. 1A to 1C, the formation pitch d and depth h of the recess 5 or the slope φ of the inclined surface is changed according to the distance from the incident end face 2. This prevents the luminance of the exit surface 3 from changing depending on the distance from the incident end surface 2.
[0013]
However, the conventional techniques as shown in FIGS. 1A to 1C have the following problems.
1. There is a region where it is difficult for light to reach behind the inclined surface 5b when viewed from the incident end face 2. Therefore, even if the formation pitch d is reduced, the direction conversion efficiency does not increase, and the brightness of the emission surface 3 is likely to be uneven.
[0014]
2. Direction control in the plane parallel to the incident end face 2 is not sufficient. For example, in FIG. 1A, when the propagation directions of the light beams G1 and G2 are parallel to the exit surface 3 but not perpendicular to the entrance end surface 2, the exit lights G1 ′ and G2 ′ are in the right direction when viewed from the entrance end surface 2. Or it will diverge to the left. A light component that is not perpendicular to the incident end face 2 exists in the actual light guide plate. Therefore, it is difficult to direct the emitted light in a spatially desirable angle or angle range (perpendicular to both the incident end face 2 and both parallel directions).
[0015]
3. Since the direction change for generating the light toward the emission surface 3 is performed once by reflection (slope 5a), light leakage from the back surface 4 is likely to occur. That is, the total reflection condition is easily broken at the time of reflection for direction change. For example, in order to direct the light beams G1 and G2 substantially in the front direction, the internal incident angle θ is set to about 45 degrees. This is almost the same as the critical angle of a typical material, acrylic resin-air. Therefore, a considerable part of the light propagating slightly downward leaks from the slope 5a.
[0016]
Therefore, the present inventor previously proposed a light guide plate having a large number of micro-reflectors having projections as shown in FIG. 2B on the back surface, and application to the surface light source device and the liquid crystal display device. (Japanese Patent Application No. 11-38977). FIG. 2A is a perspective view illustrating the optical path of the internal input light by enlarging the periphery of the micro-reflector. For convenience of explanation, the size of the micro reflector is exaggerated.
[0017]
As shown in FIG. 2A, the micro reflector 120 is formed on the back surface 114 of the light guide plate 100 so as to protrude from the general surface. The micro reflector 120 illustrated here has a block shape having six surfaces 121, 122, 123, 124, 127, 128.
[0018]
The surfaces 121 and 122 are slopes that provide a guide for smoothly performing light input for changing directions. Faces 121 and 122 meet at 嶺 126. On the other hand, the surfaces 123 and 124 are inclined surfaces that perform reflection twice for direction change and generate internal output light. Surfaces 123 and 124 meet at 嶺 125. The surfaces 127 and 128 are side walls that limit the width of the micro reflector 120. The orientation direction of the micro reflector 120 is represented by the extending direction of the ridge 125. The orientation direction of the micro-reflector 120 is aligned with the main input direction (arrival direction) of light, so that the input light to the micro-reflector is substantially maximized, and thus the direction changing efficiency is also substantially maximized.
[0019]
In FIG. 2A, the input light is represented by light rays H <b> 1 and H <b> 2 that are substantially perpendicular to the incident end face 112. However, what is actually input to the micro-reflector 120 is not exactly light parallel to the general surface of the back surface 114 but light traveling slightly downward. Light that is exactly parallel to the general surface of the back surface 114 or light that approaches the exit surface 113 travels to the back without being input to the micro-reflector 120. That is, unlike the concave portion (see FIG. 1), the micro reflector 120 does not prevent the light from traveling and does not create a region where it is difficult for light to reach.
[0020]
When viewed from the standpoint of the rays H1 and H2, the slopes 123 and 124 form valleys. Coral 125 corresponds to the valley bottom. This valley is gradually narrower and shallower. Therefore, the lights H1 and H2 entering the valley are almost always first internally reflected by one slope 123 or 124, and then internally reflected again by the other slope 124 or 123.
[0021]
As a result, the traveling direction of the light is changed by 2 degrees, and the internal output lights J1 and J2 toward the emission surface 113 are generated. The traveling directions of the internal output lights J1 and J2 can be controlled in a considerable range by adjusting the direction (spatial direction) of the inclined surfaces 123 and 124. For all the micro-reflectors, the slopes 123 and 124 so that the internal output lights J1 and J2 generated from the input lights H1 and H2 from the main light arrival directions substantially coincide with the normal direction set up on the emission surface 113. If the azimuth is adjusted, the exit light 113 can be obtained from the entire exit surface 113, which is almost a parallel light beam directed in the front direction.
[0022]
However, the light guide plate improved as described above or the surface light source device to which the light guide plate is applied still have a problem that is desired to be solved. That is, when applied to a front light type liquid crystal display device, there is an unsatisfactory point in display contrast and resolution. This will be described with reference to FIG.
[0023]
As is well known, in the front lighting arrangement, the light supplied to the liquid crystal display panel through the emission surface of the light guide plate of the surface light source device returns to the light guide plate with an intensity distribution corresponding to display information. Although the return light is emitted from the back surface of the light guide plate, a part of the light enters the micro reflector from the front direction. This is indicated by R1 and R2 in FIG.
[0024]
Here, since the microreflector 120 has the shape shown in FIG. 2B, the internal incident position of the return lights R1 and R2 to the microreflector 120 is almost any slope (in FIG. 3). The incident on the slopes 121 and 122 is exemplified). As a result, the return lights R1 and R2 are bent and emitted as illustrated in S1 and S2. Naturally, the light that is bent and emitted in this manner lowers the display contrast, and also causes a decrease in the sharpness of the display information (blurred display image).
[0025]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art. That is, one object of the present invention is to improve the light guide plate for emitting light introduced from the side end face (incident end face) from the exit face, making it difficult for the area to reach the light and easily controlling the exit direction. By adopting a simple light guide plate, it is possible to efficiently generate illumination light whose emission direction is controlled in a plane perpendicular to and parallel to the incident end face without using a direction modifying element such as a prism sheet. Provide surface light source device There is to be.
[0027]
The present invention No Another object is to provide a liquid crystal display device that is easy to observe from a desired direction by applying the surface light source device to backlighting or front lighting for a liquid crystal display device. Another object is to prevent deterioration of the contrast and sharpness of the display image, particularly when applied to front lighting.
[0028]
[Means for Solving the Problems]
By adopting the basic concept of providing a number of plate-shaped micro-reflectors on the back of the light guide plate and changing the direction by two internal reflections by a pair of slopes adjacent to the plate-shaped top surface. Solve the above technical problems.
[0032]
Book The invention improves a surface light source device including a light guide plate having at least one primary light source, two major surfaces providing an exit surface and a back surface, and a side end surface for introducing light from the primary light source.
[0033]
In the surface light source device according to the present invention, the back surface of the light guide plate includes a plurality of micro reflectors for changing the light traveling direction, and each micro reflector projects in a plateau shape from a general surface on which the back surface extends. Each microreflector provides a flat bottom surface and a valley adjacent to the bottom surface.
[0034]
And the bottom face of each micro reflector extends substantially parallel to the general surface on which the rear surface of the light guide plate extends. Further, the valley of the micro reflector includes the first slope and the second slope, and is formed so that the width becomes narrower and shallower as the distance from the bottom surface increases. Thereby, the internal input light that has arrived at the valley of the micro-reflector is internally reflected by one of the first slope and the second slope, and then internally reflected by the other slope, toward the exit surface of the light guide plate. Internal output light is generated. The extending direction of the valley bottom is So that it almost coincides with the main arrival direction of the internal input light to the valley, It has a distribution that changes depending on the position on the back Ru .
[0035]
Light may be introduced into the light guide plate from a plurality of different directions. In this case, a large number of micro-reflectors are grouped according to the light introduction made from the plurality of directions, and the micro-reflectors belonging to each group generate internal output light by sharing corresponding to the grouping. It is preferably oriented so that it does.
[0036]
Such an improved surface light source device can be applied to a surface light source device that illuminates a liquid crystal panel. In particular, when applied to a front light type liquid crystal display device provided with a surface light source device that illuminates the liquid crystal panel from the front, bending emission of return light from the liquid crystal display panel (see FIG. 3 and related description) is reduced. Therefore, there is an advantage that the display contrast and the clearness of the display image are not impaired.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
(1) First embodiment
4A and 4B show a schematic arrangement of the first embodiment of the present invention. 4A is a plan view of the light guide plate viewed from the back side, and FIG. 4B is a side view of the light guide plate viewed from the left in FIG. 4A.
[0038]
4A and 4B, one side end surface of the light guide plate 10 made of a transparent material such as acrylic resin, polycarbonate (PC), or cycloolefin resin provides the incident end surface 12. . A rod-shaped primary light source (cold cathode tube) L <b> 1 is disposed along the incident end face 12 and supplies light to the incident end face 12. One of the two major surfaces 13 and 14 of the light guide plate 10 is an emission surface 13. A number of micro reflectors 20 are provided on the other surface (back surface) 14.
[0039]
A well-known liquid crystal panel PL is arranged outside the emission surface 13 to constitute a backlight type liquid crystal display device. In addition, a dimension display is an illustration to the last and a unit is mm.
[0040]
The light emitted from the primary light source L1 is introduced into the light guide plate 10 through the incident end face 12. When the light propagating in the light guide plate 1 enters the micro reflector 20, the light is mainly reflected twice in the micro reflector 20, and light directed toward the emission surface 13 is generated. Since the micro-reflector 20 is a direction changing means, it can be said that “the input light to the micro-reflector 20 is converted into the internal output light directed to the exit surface 13”. Details of the shape and operation of each micro-reflector 20 will be described later.
[0041]
5 (a) and 5 (b) are diagrams for explaining the arrangement of the micro-reflectors 20 in the present embodiment, and FIG. 3 (a) shows an extraction of the arrangement around the circle A in FIG. 2 (a). In FIG. 3B, the arrangement around the circle B in FIG. 2A is extracted and depicted. In this example, the formation pitches p and q in the width direction and the depth direction of the micro reflector 20 are p1 = q1 = 220 μm in the vicinity of the circle A, whereas p2 = q2 = 130 μm in the vicinity of the circle B. ing.
[0042]
Although the numerical values of the pitches p and q are merely examples, the formation density of the micro reflectors 20 is set to be relatively small in an area relatively close to the incident end face 12 and relatively large in an area relatively far from the incident end face 12. Yes. Although not shown, the formation pitch of the entire rear surface 14 is gradually reduced according to the distance from the incident end surface 12. In other words, the formation density (coverage) gradually increases according to the distance from the incident end face 12. Specific numerical values are determined by design. For example, the value is about 10% in the area A close to the incident end face 12 and about 30% in the area B far away. In this way, by increasing or decreasing the coverage, the luminance is made uniform over the entire emission surface 13. In addition, the definition of a coverage is as follows.
Coverage = S / (p × q)
Here, S is a cross-sectional area obtained by cutting the micro-reflector along the general surface of the back surface 14, and p and q are formation pitches in the width direction and the depth direction. The “general surface of the back surface 14” is a plane on which the back surface 14 is on the assumption that the micro-reflector is removed.
[0043]
Each micro-reflector 20 forms a plate-like projection having a substantially diamond-shaped cross section. The size of the outline (diamond) is such that it is difficult to recognize individually when visually observed. In addition, since the size of each micro reflector 20 corresponds to the lower limit of the formation pitch, it is preferable that the size is small from this viewpoint. This is because when the formation pitch is large, it is easy to observe as a bright and dark pattern. An example of the size is r = about 80 μm and s = about 120 μm in FIG.
[0044]
It should be noted here that in order to equalize the direction of turning, it is avoided that the micro-reflector 20 is aligned along the main light arrival direction (in this example, substantially perpendicular to the incident end face 12). It is that you are. That is, the arrangement of the micro reflectors 20 is preferably deviated from an accurate two-dimensional matrix. Such an arrangement is also advantageous in making the microreflector arrangement as obscure as possible.
[0045]
Next, the direction changing action of the micro reflector 20 will be described with reference to FIGS. This description also applies to the microreflector of the light guide plate employed in other embodiments.
FIG. 6 shows a typical path that is introduced into the light guide plate 10 and exits from the exit surface 13 via the micro reflector 20. For convenience of explanation, the size of the micro reflector 20 is exaggerated. The orthogonal coordinates O-xyz are set so that the xz plane is substantially parallel to the incident end face 12 and the xy plane is substantially parallel to the exit face 13.
[0046]
Further, here, a light diffusing sheet DF is additionally disposed along the emission surface 13 of the light guide plate 10 with respect to the arrangement of FIG. 4, and is a reflective sheet having specular reflection or irregular reflection along the back surface 14. RF is additionally arranged. Illustration of the liquid crystal display panel PL is omitted.
7 (a), 7 (b), and 7 (c) show how the micro-reflector 20 changes direction in three directions (in the + z-axis direction, + x-axis direction, and + y-axis in order) in the arrangement of FIG. It is a figure drawn from (direction).
[0047]
As can be seen from these drawings, the micro-reflector 20 is formed so as to protrude from the general surface of the back surface 14 of the light guide plate 10. Each micro reflector 20 has a plateau shape having five surfaces 21 to 25. The redirecting of the input light is achieved mainly by the surfaces 22 and 23. Therefore, the surfaces 22 and 23 are inclined with respect to any of the xy plane, the yz plane, and the zx plane, and a valley is formed inside the micro reflector 20. A valley bottom (an ridge as viewed from the outside) 26 extending from the position indicated by the reference numeral 26a to the position indicated by the reference numeral 26b corresponds to an intersection formed by the slopes 22 and 23 meeting each other.
[0048]
In accordance with a feature of the present invention, a flat surface 21 is provided adjacent to the valley including the slopes 22,23. The surface 21 forms a “bottom surface” adjacent to the valley, and is provided in front of the inclined surfaces 22 and 23 (on the light input side) so as to accept a wide range of light input to the surfaces 22 and 23 and promote a change of direction. Further, as will be described later, the bottom surface 21 extends in parallel with the general surface on which the back surface 14 rides in order to enhance the applicability to the front light type lighting. Therefore, the distance between the general surface and the bottom surface 21 is the “height” of the plate-shaped micro reflector 20. The height of each micro reflector 20 is in the range of about 10 μm to 30 μm, for example.
[0049]
Further, the ratio S21 / S20 can be freely adjusted, where S20 is the area where the entire micro-reflector 20 is projected onto the same general surface, and S21 is the area where the bottom surface 21 is projected onto the same general surface. By making this ratio S21 / S20 sufficiently large, it is possible to secure a wide incident route to the slopes 22 and 23 and to improve the applicability to front lighting (see the embodiment of Brother 6).
[0050]
In that sense, the ratio S21 / S20 is preferably 0.3 or more. In particular, 0.4 to 0.6 is an example of a practical range. However, it should be noted that if S21 / S20 is too close to 1.0, the overall size becomes excessive, and it becomes easy to visually recognize and it is difficult to increase the distribution density (number density).
[0051]
Here, another important point is that the valley bottom 26 approaches the general surface of the back surface 14 from the start end 26a on the bottom surface 21 side toward the end end 26b. In other words, the valley including the slopes 22 and 23 becomes gradually narrower and shallower as the distance from the bottom surface 21 increases.
[0052]
It is preferable that the surfaces 24 and 25 adjacent to the bottom surface 21 are substantially vertical at a portion corresponding to a plateau-shaped “cliff”. This is to prevent the return light from entering the surfaces 24 and 25 when applied to the front light type liquid crystal display device.
[0053]
The orientation direction of the micro reflector 20 can be represented by the extending direction of the valley bottom 26. Here, in consideration of the orientation, as shown in FIG. 7A, the orientation of the micro reflector 20 is represented by a vector from the start end 26a on the surface 21 side to the end 26b.
[0054]
The orientation direction of the micro-reflector 20 (vector 26a → 26b) is aligned with the main input direction (arrival direction) of light. ing . As a result, the input to the micro-reflector 20 is substantially maximized, and the direction change efficiency is substantially maximized accordingly.
[0055]
In FIG. 6 and FIG. 7, the input light from the main light arrival direction is represented by the light beam H10. In the arrangement employing the primary light source L1 (see FIG. 4), the light beam H10 is substantially perpendicular to the incident end face 12. However, what is actually input to the micro-reflector 20 is not exactly light parallel to the general surface (xy plane) of the back surface 14 but light traveling downward (light approaching the back surface 14). Light that is exactly parallel to the general surface of the back surface 14 or light that approaches the exit surface 13 travels to the back without being input to the micro-reflector 20. That is, unlike the concave portion (see FIG. 1), the micro-reflector 20 does not prevent the light from traveling and does not create a region where it is difficult for light to reach.
[0056]
Since the valley including the slopes 22 and 23 becomes narrower and shallower as the distance from the bottom surface 21 increases, the light H10 that has entered the valley is first internally reflected by one slope 22 or 23, and then the other slope 23 or 23 At 22 again, it is internally reflected again. As a result, the traveling direction of the light is three-dimensionally changed twice, and the internal output light IO directed toward the emission surface 13 is generated.
[0057]
The traveling direction of the internal output light IO can be controlled within a considerable range by adjusting the direction (spatial direction) of the inclined surfaces 22 and 23. For all the micro-reflectors, if the orientations of the inclined surfaces 22 and 23 are adjusted so that the internal output light IO generated from the input light H10 from the light arrival direction substantially coincides with the normal direction set up on the emission surface 13. Thus, output light J10 heading substantially in the front direction is obtained from the entire emission surface 13.
[0058]
Further, by adjusting the orientation and orientation of the inclined surfaces 22 and 23 (extending direction of the valley bottom 26), it is possible to generate a convergent output light beam that aims at one point away from the exit surface 13. The orientation of the slope 22 and the orientation of the slope 23 are not necessarily symmetric with respect to the valley bottom 26. Due to this asymmetry, the azimuth controllability of the output light beam is extended.
[0059]
Since the direction change by the micro-reflector 20 is performed three-dimensionally, the direction can be controlled both in the zx plane parallel to the incident end face 12 and in the vertical yz plane. Since the direction change is performed by two reflections, the direction change angle per time is generally small. Therefore, the incident angle to the inclined surfaces 22 and 23 is generally sufficiently larger than the critical angle, and light leakage is unlikely to occur.
The outline of the path of the light beam H10 shown in FIGS. 6 and 7A to 7C is summarized as follows. First, the light beam H <b> 10 introduced into the light guide plate 10 from the incident point “a” on the incident end face 12 approaches one micro reflector 20. Here, when viewed from the standpoint of the light beam H10, the bottom surface 21 of the micro-reflector 20 appears to be an entrance that accepts incident light in front of the slopes 22 and 23 with a wide frontage. The light beam H10 that has entered the micro-reflector 20 is incident on one of the inclined surfaces 22 and 23 (or 23) at a considerably large incident angle, and is almost totally reflected (point b). Next, internal reflection (total reflection) is similarly performed on the other inclined surface 23 (or 22) (point c), and an internal output IO is obtained.
[0060]
The internal output light IO is output from the emission surface 13 and becomes output light J10 (point d). In this example, the output light J10 further enters the light diffusion sheet DF (point e), exits there (point f), and is supplied to, for example, the liquid crystal display panel PL (see FIG. 4). The light diffusion sheet DF is provided as necessary in order to prevent fine light and dark unevenness corresponding to the difference between the position where the micro reflector 20 is present and the position where the micro reflector 20 is not present due to weak light diffusion.
[0061]
As described above, the traveling direction of the internal output light IO or the output light J10 can be controlled within a considerable range by adjusting the orientations of the inclined surfaces 22 and 23.
[0062]
The input light to the micro reflector 20 includes a component that is internally reflected by the bottom surface 21. Most of such light is also converted to internal output light after being reflected twice by the inclined surfaces 22 and 23. The traveling direction is slightly different from the internal output light IO that does not pass through the reflection by the bottom surface 21. As a result, the traveling direction of the corresponding output light is distributed around the traveling direction of the main output light J10 (substantially the front direction in this example).
[0063]
In addition, there is some light leakage from the back surface 14 including the micro reflector 20. The reflection member RF has a function of returning this light leakage to the light guide plate 10. Thus, the position when the light passing through the reflecting member RF escapes from the emission surface 13 is very diverse, and it is considered that the correspondence with the position of the micro reflector 20 is almost lost.
[0064]
Therefore, the inclusion of these lights in addition to the main output light J10 in the overall output light is rather advantageous in preventing fine light and dark unevenness corresponding to the difference between the position where the micro reflector 20 is present and the position where it is absent. That is.
[0065]
(2) Second embodiment
The schematic arrangement of the second embodiment is similar to the schematic arrangement of the first embodiment shown in FIGS. 4A and 4B, but the employed light guide plate is different from the first embodiment. In this embodiment, the light guide plate 30 shown in FIG. The light guide plate 30 is made of a transparent material such as acrylic resin, polycarbonate (PC), or cycloolefin resin, and one side end face thereof provides an incident end face 32.
[0066]
A rod-shaped primary light source (cold cathode tube) L <b> 2 is disposed along the incident end face 32 and supplies light to the incident end face 32. It should be noted here that the length of the light emitting portion of the cold cathode tube L2 is slightly shorter than the length of the incident end face 32. Both ends are electrode portions EL1 and EL2, and do not emit light. Such a design is often employed in order to prevent the electrode portions EL1 and EL2 at both ends from protruding.
[0067]
A large number of micro reflectors 20 are provided on the back surface 34. The shape and size of each micro reflector 20 may be the same as that of the light guide plate 10. This point is the same in the third to sixth embodiments. The arrangement and orientation of a large number of micro reflectors 20 have the following characteristics.
[0068]
1. The coverage tends to increase according to the distance from the incident end face 32. This prevents a change in luminance depending on the distance from the incident end face 32 from appearing on the exit surface.
[0069]
2. In the corner areas C and D close to the electrode portions EL1 and EL2, the micro-reflectors 20 are particularly arranged at a high density. This arrangement prevents dark areas corresponding to the corner areas C and D from appearing on the exit surface together with the following four orientations.
[0070]
3. In most of the back surface 34, the orientation of the micro-reflector 20 is substantially perpendicular to the incident end surface 32 and aligned in the depth direction. That is, the bottom surface 21 of each micro-reflector 20 is located closer to the incident end surface 32 than the valley including the inclined surfaces 22 and 23.
[0071]
4). In the corner areas C and D, the orientation of the micro reflector 20 is inclined with respect to the incident end face 32, and the bottom face 21 is directed to the light emitting portion of the cold cathode tube L2. This makes the light arrival direction correspond to the orientation of the micro-reflector 20 and increases the direction change efficiency.
5. In both side portions 35 and 36 excluding the corner areas C and D, the orientation of the micro reflector 20 is inclined by a small angle with respect to the incident end face 32, and the bottom face 21 is directed to the light emitting part of the cold cathode tube L2. As in 4 above, this corresponds to the direction of arrival of light and the orientation of the micro-reflector 20 to increase the direction change efficiency.
[0072]
6). A large number of micro-reflectors 20 do not have an order that is arranged in a straight line. Thereby, the micro reflector 20 is made less noticeable. Further, when incorporated in a liquid crystal display, the occurrence of moire fringes due to the overlapping relationship with the matrix electrode arrangement is prevented.
[0073]
(3) Third embodiment
The schematic arrangement of the third embodiment is similar to the schematic arrangement of the first and second embodiments, but the employed light guide plate is different from them. In the present embodiment, the light guide plate 40 shown in FIG. 9 is employed. The light guide plate 40 is made of a transparent material such as acrylic resin, polycarbonate (PC), or cycloolefin resin, and two side end surfaces provide incident end surfaces 42a and 42b.
[0074]
Rod-shaped primary light sources (cold cathode tubes) L3 and L4 are arranged along the incident end faces 42a and 42b, and supply light to the incident end faces 42a and 42b, respectively.
[0075]
A large number of micro-reflectors 20 are provided on the back surface 44. The arrangement and orientation have the following characteristics.
1. The coverage and orientation of the microreflector are designed as follows. First, assuming only light supply from one primary light source L3, the distribution of coverage and orientation (referred to as distribution 1) is designed so that the luminance on the entire emission surface is uniform. Next, assuming only light supply from the other primary light source L4, the distribution of coverage and orientation (referred to as distribution 2) is designed so that the luminance on the entire emission surface is uniform. The distribution 1 and the distribution 2 are overlapped to obtain a coverage and orientation distribution (distribution 1 + distribution 2) in the present embodiment.
[0076]
Micro-reflectors 20 corresponding to distribution 1 form a first group, and micro-reflectors 20 corresponding to distribution 2 form a second group. It is preferable that the micro reflectors 20 constituting each group have approximately the same number, approximately the same shape, and approximately the same size.
[0077]
The coverage by the group 1 increases according to the distance from the incident end face 42a, while the coverage by the second group tends to increase according to the distance from the incident end face 42b. Therefore, as a whole, the gradients of distribution 1 and distribution 2 tend to cancel each other. In the illustrated example, a case with a substantially uniform coverage is depicted.
[0078]
The orientation of the micro reflector 20 is aligned substantially perpendicular to the incident end face 42. However, regarding the orientation, the bottom surface 21 of the group 1 micro-reflectors 20 is directed to the incident end face 42a, and the bottom face 21 of the group 2 micro-reflectors 20 is directed to the incident end face 42b.
[0079]
Note that such a grouping method according to the light introduction direction is applicable even when the light introduction directions are three or more. For example, when light is supplied to the light guide plate from four directions using four end faces, it is considered that there are four light input directions, and the covering rule distribution and orientation distribution of the micro reflector are designed by dividing into four groups. Just do it. As described in the example of the two groups, the entire coverage rule distribution and the orientation distribution distribution may be a superposition of the coverage rule distribution and the orientation distribution of the micro reflectors belonging to each group.
[0080]
2. Similar to the second embodiment, there is no order in which a large number of micro-reflectors 20 are arranged in a straight line. Thereby, the micro reflector 20 is made less noticeable. Further, when incorporated in a liquid crystal display, the occurrence of moire fringes due to the overlapping relationship with the matrix electrode arrangement is prevented.
[0081]
(4) Fourth embodiment
The schematic arrangement of the fourth embodiment is similar to the schematic arrangement of the first, second, and third embodiments, but the employed light guide plate and primary light source are different from them. In the present embodiment, the light guide plate 50 and the primary light source L5 shown in FIG. 10 are employed. The light guide plate 50 is made of a transparent material such as acrylic resin, polycarbonate (PC), or cycloolefin resin, and a concave portion 52a formed at the center of one side end surface 52 provides an incident end surface.
[0082]
The primary light source L5 is a point light source using, for example, one or a plurality of LEDs (light emitting diodes). Here, the “point light source” is a light source having a light emission area much smaller than the spread of the incident end face 52. The primary light source L5 is disposed so as to supply light to the light guide plate through the recess 52a. A large number of micro reflectors 20 are provided on the back surface 54. The arrangement and orientation have the following characteristics.
[0083]
1. The coverage tends to increase according to the distance from the recess 52a. This prevents a change in luminance depending on the distance from the recess 52a (point light source L5) from appearing on the exit surface.
2. Over the entire back surface 54, the orientation of the micro-reflector 20 is determined radially from the recess 52a (light emission position of the point light source). The bottom surface 21 of each micro reflector 20 is directed substantially toward the recess 52a.
[0084]
3. When the radiation characteristic of the point light source L5 has directivity in the front direction, the coverage of the micro reflector 20 may be increased around the side end face 52. In particular, for the corner areas E and F, the coverage is preferably increased.
[0085]
4). A large number of micro-reflectors 20 do not have an order that is arranged in a straight line. Thereby, the micro reflector 20 is made less noticeable. Further, when incorporated in a liquid crystal display, the occurrence of moire fringes due to the overlapping relationship with the matrix electrode arrangement is prevented.
[0086]
(5) Fifth embodiment
The schematic arrangement of the fifth embodiment is similar to the above-described embodiments, particularly the schematic arrangement of the fourth embodiment, but the light guide plate and the primary light source employed are different from those. In the present embodiment, the light guide plate 60 shown in FIG. 11 and the two primary light sources L6 and L7 are employed. The light guide plate 60 is made of a transparent material such as acrylic resin, polycarbonate (PC), or cycloolefin resin, and concave portions 62a and 62b formed at two locations on one side end surface 62 provide an incident end surface.
[0087]
The primary light sources L6 and L7 are point light sources similar to those used in the fourth embodiment, and are arranged so as to supply light to the light guide plate through the recesses 62a and 62b, respectively. A large number of micro reflectors 20 are provided on the back surface 64. The arrangement and orientation have the following characteristics.
[0088]
1. The coverage and orientation are designed so that a change in luminance does not appear on the exit surface in consideration of the positional relationship with the recesses 62a and 62b.
[0089]
First, assuming only light supply from one primary light source L6, the distribution of coverage and orientation (referred to as distribution 3) is designed so that the luminance on the entire emission surface is uniform. A group of micro reflectors according to this distribution 3 forms one group (referred to as group 3).
[0090]
Next, assuming only light supply from the other primary light source L7, a distribution of coverage and orientation (referred to as distribution 4) is designed so that the luminance on the entire emission surface is uniform. A group of micro reflectors according to this distribution 4 forms another group (referred to as group 4). The distribution 3 and the distribution 4 are overlapped to obtain a distribution of coverage and orientation (a distribution 3 followed by the group 3 + a distribution 4 followed by the group 4) in the present embodiment.
[0091]
The coverage by the distribution 3 increases according to the distance from the primary light source L6, while the coverage by the distribution 4 tends to increase according to the distance from the primary light source L7. Therefore, as a whole, the gradients of distribution 3 and distribution 4 tend to cancel each other. In the illustrated example, a case with a substantially uniform coverage is depicted.
[0092]
The orientation of the micro-reflector 20 is determined radially from the recess 62a according to the distribution 3 for the group 3 and radially from the recess 62b according to the distribution 4 for the group 4. The bottom surface 21 of each microreflector 20 of the former (group 3) is on the recess 62a side, and the bottom surface 21 of each microreflector 20 of the latter (group 3) is on the recess 62b side.
[0093]
As described above, even when light is supplied from a plurality of locations on one end face and there are a plurality of main light introduction directions to the micro reflector, the same grouping as described in the third embodiment can be performed. is there. In the present embodiment, an example is shown in which light is supplied from two locations on one end face. However, if light is supplied from three or more locations, the number of groups is increased accordingly and each group is increased. It is sufficient to design the coverage distribution and orientation distribution.
[0094]
2. A large number of micro-reflectors 20 do not have an order that is arranged in a straight line. Thereby, the micro reflector 20 is made less noticeable. Further, when incorporated in a liquid crystal display, the occurrence of moire fringes due to the overlapping relationship with the matrix electrode arrangement is prevented.
[0095]
(6) Sixth embodiment
As shown in FIG. 12, the surface light source device of the present invention is also applicable to front lighting of a front light type liquid crystal display. This is the sixth embodiment.
[0096]
The light guide plate 70 of the surface light source device used for front lighting is arranged on the front surface (observation surface side) of the liquid crystal panel. The liquid crystal panel includes a scattering film (light diffusion sheet) 101, a polarizing plate 102, a first glass substrate 103, a color filter 104, a liquid crystal cell 105, a specular reflection electrode 106, and a second glass substrate 107. The color filter 104 has three primary color regions R, G, and B. Since the structure and operating principle of such a liquid crystal panel are well known, detailed description thereof will be omitted.
[0097]
The light guide plate 70 and the primary light source (not shown) may follow any of the first to fifth embodiments.
[0098]
The light guide plate 70 used for front lighting is arranged so that the emission surface 73 faces the liquid crystal panel. As indicated by symbols H, J, and K, when the light H propagating through the light guide plate 70 is input to the micro reflector 20, it is converted into the internal output light J by the internal reflection twice described above. The internal output light J is emitted substantially perpendicularly from the emission surface 73 and enters the liquid crystal panel.
[0099]
The internal output light J is reflected by the specular reflection electrode 106 through the scattering film (light diffusion sheet) 101, the polarizing plate 102, the first glass substrate 103, the color filter 104, and the liquid crystal cell 105. The reflected light reaches the polarizing plate 102 through the liquid crystal cell 105, the color filter 104, and the glass substrate 103 again. Transmission / cutoff of the polarizing plate 102 is determined depending on ON / OFF (polarization state) of the specular reflection electrode 106 of the corresponding pixel. If the specular reflection electrode 106 allows transmission through the polarizing plate 102, it is emitted as display light K from the back surface 74 through the scattering film (light diffusion sheet) 101 and the light guide plate 70.
[0100]
What is important here is that most of the light that encounters the micro-reflector 20 on the back surface 74 is emitted from the flat bottom surface 21 almost in the front direction. FIG. 13 shows this state. Since the micro reflector 20 has a trapezoidal shape as shown in FIGS. 7A to 7C and FIG. 13, the micro reflector 20 returns from the liquid crystal display panel into the light guide plate 70 and encounters the micro reflector 20. The internal incident positions of the return lights R10 and R20 come on the bottom surface 21 with a high probability. Since the bottom surface 21 is substantially parallel to the general surface of the back surface 74, emission from the bottom surface 21 is equivalent to emission from a portion of the back surface 74 where the micro-reflector 20 is not present.
[0101]
Since the light supply to the liquid crystal display panel is normally performed substantially in the front direction, the return lights R10 and R20 enter the bottom surface 21 substantially perpendicularly and become the emitted lights S10 and S20 in the substantially front direction without bending. This prevents a decrease in display contrast and a decrease in display information sharpness (blurred display image) (see FIG. 3 and the related description and comparison).
[0102]
It is preferable that the exit surface of the light guide plate used in the embodiments described above, particularly the sixth embodiment, is covered with an antireflection layer. FIG. 14 shows a cross section when the antireflection layer is provided on the light exit surface of the light guide plate. The antireflection layer AR is made of, for example, MgF 2 (refractive index: 1.38), and the thickness t is, for example, 99.6 μm. The light guide plate is made of polycarbonate (PC) (refractive index: 1.58).
[0103]
A part of the light incident on the exit surface is partially reflected and partially transmitted by the PC-MgF2 interface and the MgF2-air interface. As is well known, when the thickness, refractive index, wavelength, and incident angle of the antireflection layer AR are set such that the transmitted light T is strengthened by interference and the reflected light R is weakened by interference, Functions as a prevention layer.
[0104]
FIG. 15 shows the reflectance (100% -emission rate) under the above conditions as a function of wavelength for vertically incident light, together with the case without the antireflection layer. As understood from the graph, in the case without the antireflection layer (NCT), the reflectance is almost constant 3.8%. On the other hand, in the case (CT) in which the antireflection layer is used, a low reflectance of about 1% to 2% is obtained in a wavelength region of about 400 μm to 780 μm.
[0105]
Therefore, if such an antireflection layer is provided on the exit surface of the light guide plate used in the embodiments, particularly the sixth embodiment, the exit from the exit surface becomes smooth, and the noise derived from the reflected light is reduced. The
[0106]
【The invention's effect】
As described above, according to the present invention, the micro-reflectors distributed on the back surface of the light guide plate fulfill an efficient direction changing function mainly based on the internal reflection twice. The direction of the internal output light at that time can be adjusted by the orientation of the slope pair included in the valley adjacent to the flat surface of the micro reflector.
[0107]
Therefore, unlike the direction change that relies on scattering and diffusion, light emission in an unnecessary direction is prevented. Further, the emission in the front direction or the peripheral direction can be achieved without a prism sheet.
[0108]
Furthermore, even if the front lighting arrangement is adopted for an object to be illuminated such as a liquid crystal display panel, the degree to which the path of the return light from the object to be illuminated is disturbed by the micro reflector is reduced. In particular, when applied to a front-lit type liquid crystal display device, it is possible to prevent deterioration in contrast and sharpness of a display image.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams for explaining a conventional technique, in which FIG. 1A illustrates the principle of an edge lighting effect, and FIGS.
FIGS. 2A and 2B are diagrams for explaining the prior art (related invention according to the prior application), in which FIG. 2A is an enlarged view of the periphery of the micro-reflector and a perspective view for explaining the optical path of the internal input light, and FIG. It is the perspective view which showed the shape of the reflector.
FIG. 3 is a diagram illustrating a problem when the prior art shown in FIG. 2 is applied to front lighting.
4A and 4B are schematic views of a first embodiment of the present invention, in which FIG. 4A is a plan view seen from the back side of a light guide plate, and FIG. 4B is a side view seen from the left in FIG. Each one is represented.
5A shows an arrangement of the micro-reflectors 20 in the first embodiment in the vicinity of the circle A in FIG. 4A, and FIG. 5B shows the vicinity of the circle B in FIG. 4A. The sequence of is extracted and drawn.
FIG. 6 is a diagram for explaining a typical route (main route) until input light to the light guide plate is emitted from the emission surface through the direction change by the micro reflector.
7 is a diagram illustrating the direction change of the micro-reflector 20 from three directions in the arrangement of FIG. 6, where (a) is from the + z-axis direction, (b) is from the + x-axis direction, and (c). Is a drawing from the + y-axis direction.
FIG. 8 is a plan view for explaining a micro-reflector arrangement in the second embodiment.
FIG. 9 is a plan view for explaining a micro-reflector arrangement in the fourth embodiment.
FIG. 10 is a plan view for explaining a micro-reflector arrangement in the second embodiment.
FIG. 11 is a plan view for explaining a micro-reflector arrangement in the fifth embodiment.
FIG. 12 is a cross-sectional view illustrating a sixth embodiment applied to front lighting of a front light type liquid crystal display.
FIG. 13 is a diagram for explaining advantages when the present invention is applied to front lighting.
FIG. 14 is a diagram for explaining the action of an antireflection film.
FIG. 15 is a graph illustrating characteristics of an antireflection film.
[Explanation of symbols]
1, 10, 30, 40, 50, 60, 70, 100 Light guide plate
2, 12, 32, 42a, 42b Incident end face
3, 13, 73 Outgoing surface (one major surface)
4, 14, 34, 44, 54, 64, 74 Back (the other major surface)
5 recesses
5a, 5b slope
20, 120 Micro reflector
21 Bottom)
22, 23, 121-124 Slope
24, 25 Sharp surface
26 Valley bottom
26a The beginning of the valley floor
26b End of valley bottom
35, 36 Sides of light guide plate
52, 62 Side end face of light guide plate
52a, 62a, 62b Recessed part (incident end face)
101 scattering film (light diffusion sheet)
102 Polarizing plate
103, 107 Glass substrate
104 Color filter
105 Liquid crystal cell
106 Specular reflection electrode
C, D, E, F Corner area of light guide plate
L, L1-L7 Primary light source
LP LCD panel

Claims (7)

In a surface light source device comprising at least one primary light source, a light guide plate with two major surfaces providing an exit surface and a back surface, and a side end surface for introducing light from the primary light source ;
The back is provided with a number of micro reflectors for changing the direction of light travel,
Each micro-reflector forms a protrusion protruding in a plateau form from a general surface extending from the back surface,
Each micro-reflector provides a flat bottom surface inside and a valley adjacent to the bottom surface,
The bottom surface is provided on the light input side of the valley, and extends substantially parallel to a general surface from which the back surface extends,
The valley includes a first slope and a second slope, and is formed to have a tendency to become narrower and shallower as the distance from the bottom surface increases.
As a result, the internal input light that has arrived at the valley is internally reflected on one of the first slope and the second slope, and then internally reflected on the other slope, and the internal output light that travels toward the exit surface. Is generated ,
The surface light source device , wherein the extending direction of the bottom of the valley has a distribution that changes according to the position on the back surface so as to substantially coincide with the main arrival direction of the internal input light to the valley . The light introduction is made from a plurality of different directions, and the multiple micro reflectors are grouped corresponding to the light introduction made from the plurality of directions,
2. The surface light source device according to claim 1 , wherein the micro-reflectors belonging to each group are oriented so as to generate internal output light in a share corresponding to the grouping . The surface light source device according to claim 2, wherein each of the plurality of groups includes substantially the same number, substantially the same shape, and substantially the same size of microreflectors . A liquid crystal display device comprising a surface light source device for illuminating a liquid crystal panel;
The surface light source device includes a light guide plate having at least one primary light source, two major surfaces providing an emission surface and a back surface, and a side end surface for introducing light from the primary light source;
The back is provided with a number of micro reflectors for changing the direction of light travel,
Each micro-reflector forms a protrusion protruding in a plateau form from a general surface extending from the back surface,
Each micro-reflector provides a flat bottom surface inside and a valley adjacent to the bottom surface,
The bottom surface is provided on the light input side of the valley, and extends substantially parallel to a general surface from which the back surface extends,
The valley includes a first slope and a second slope, and is formed to have a tendency to become narrower and shallower with distance from the bottom surface,
As a result, the internal input light that has arrived at the valley is internally reflected on one of the first slope and the second slope, and then internally reflected on the other slope, and the internal output light that travels toward the exit surface. Is generated,
The liquid crystal display device according to claim 1, wherein the extending direction of the bottom of the valley has a distribution that varies depending on the position on the back surface so as to substantially coincide with the main arrival direction of the internal input light to the valley . A front light type liquid crystal display device comprising a surface light source device for illuminating a liquid crystal panel from the front;
The surface light source device includes a light guide plate having at least one primary light source, two major surfaces providing an emission surface and a back surface, and a side end surface for introducing light from the primary light source;
The back is provided with a number of micro reflectors for changing the direction of light travel,
Each micro-reflector forms a protrusion protruding in a plateau form from a general surface extending from the back surface,
Each micro-reflector provides a flat bottom surface inside and a valley adjacent to the bottom surface,
The bottom surface is provided on the light input side of the valley, and extends substantially parallel to a general surface from which the back surface extends,
The valley includes a first slope and a second slope, and is formed to have a tendency to become narrower and shallower with distance from the bottom surface,
As a result, the internal input light that has arrived at the valley is internally reflected on one of the first slope and the second slope, and then internally reflected on the other slope, and the internal output light that travels toward the exit surface. Is generated,
The liquid crystal display device according to claim 1, wherein the extending direction of the bottom of the valley has a distribution that varies depending on the position on the back surface so as to substantially coincide with the main arrival direction of the internal input light to the valley . The light introduction is made from a plurality of different directions, and the multiple micro reflectors are grouped corresponding to the light introduction made from the plurality of directions,
6. The liquid crystal display device according to claim 4, wherein the micro-reflectors belonging to each group are oriented so as to generate internal output light in a share corresponding to the grouping . The liquid crystal display device according to claim 6, wherein each of the plurality of groups includes substantially the same number, substantially the same shape, and substantially the same size of microreflectors .

Images